This invention relates to a method and apparatus for cutting concrete by the use of a laser, and more particularly to a method and apparatus which enables the molten slag occurring during the melt cutting of concrete by the use of a laser to be easily removed by lowering the viscosity or the molten slag and preventing the molten slag from expanding in the course of setting and which can be effectively used not merely for cutting but also for gouging and breaking the concrete by remotely controlled operation of the apparatus.
In the fields of civil engineering and construction, materials of plain concrete and reinforced concrete, materials of various metallic substances including stainless steel, and materials of non-metallic substances are generally cut and otherwise processed by use of various tools. When operations of this nature are carried out by the use of conventional mechanical tools, they prove inefficient because such tools must be changed as the materials to be treated are changed. In an extreme case, such operations turn out to be infeasible. To overcome this difficulty, highly powerful lasers have come to be adopted for performing such operations on various materials of stainless steel and other metallic substances and non-metallic substances. Persons experiencing difficulties in the cutting of concrete, therefore, may readily conceive an idea of using such a laser for the purpose of concrete cutting. Although the cutting of concrete by the use of a laser is recognized to be theoretically possible, there are problems yet to be solved in reducing the principle to practice. For example, this operation entails the disadvantage that the molten slag issuing from molten concrete assumes a glassy state and exhibits high viscosity and, on being cooled, expands and adheres fast to the walls of the gouge cut by the laser beam and becomes difficult to remove.
Thus, the cutting of concrete is still difficult even by the use of a laser. Particularly when the operation of concrete cutting by means of a laser is carried out at a site where the work conditions are harsh, the efficiency of the operation is notably degraded even to a point where the operator is exposed to danger. The work of dismantling a nuclear reactor may be cited as a case in point.
The service life of a nuclear reactor, though variable with the availability factor of the particular nuclear reactor, is generally estimated to be about 40 years. After lapse of this service life, the atomic power is decommissioned. The dismantling of the reactor is one part of the decommissioning operation. The concrete wall which has served as a biological shield concrete is also broken down. Generally, the concrete wall comprises a stainless steel plate (about 6 mm in thickness), a plain concrete layer (about 100 mm in thickness), and a reinforced concrete layer (1 to 1.5 m in thickness), sequentially from the inner side. Since it is formed of dissimilar substances, it has been necessary to use various cutting tools such as a disk cutter, grinding cutter, and scissors cutter, alternately according to the materials to be cut. Since this dismantling operation requires complicated use of cutting tools, it has been held that the operation cannot be automated.
Even after the nuclear reactor has been shut down, the biological shield concrete still retains a significant amount of residual radiation. Thus, the cutting work performed on the biological shield concrete must be carried out under remote control. Even then, the changing of various cutting tools has to be carried out manually. The fact that the tools soiled with radioactive dust must be interchanged by the human hand is most undesirable thing from the standpoint of safety.
In the circumstance, a cutting device which provides effective cutting of the concrete and particularly enables the biological shield wall of the nuclear reactor to be easily and safely cut has been desired.